The villagers who unexpectedly passed through a space 1.5 meters high

I built a steel-removing machine. To obtain iron ingots, I scare the villagers with zombies to create iron puppets and then kill the iron puppets. To ensure the efficiency of the machine, I placed 3 beds in a 332 space and left a 1*2 gap, and placed 3 villagers there. However, after some time, one of the villagers would be pushed down. So I placed another half-brick in front, but all of a sudden, one of the villagers was pushed up. Villagers cannot squat, and the collision box is 2 units high. It shouldn't be possible for them to climb up.